Fabrication of Nanotwinned Surfaces Induced by the Machining Stress of Diamond Tool

Author:Wang Bo

Supervisor:zhang zhen yu


Degree Year:2019





In virtue of its unique crystal structure,nanotwinned material possesses excellent mechanical,electronic and electrical properties.It has important application in the fields of material strengthening and electronic band engineering.In the past decade,researchers paid many attentions on the preparation of na notwinned material,and have developed a variety of preparation methods,such as pulsed electrodeposition,magnetron sputtering,dynamic plastic deformation and surface mechanical grinding treating.However,there are also many disadvantages in preparing nanotwinned materials for current methods,including harsh conditions,low efficiency and use of toxic reagents.Therefore,it is crucial to develop new approach of fabricating nanotwinned materials.In order to solve the above problems,in this paper,nanotwinned materials were fabricated by the machining stress of ultra-precision diamond tool.Two kind of novel ultra-precision diamond tools,namely macro-micro-nano integrated ultra-precision diamond tool and single-point diamond tool,were developed to fabricate nanotwinned nickel alloy and nanotwinned silicon,respectively.Nanotwinned surface of nickel alloy was induced by the indented stress of the macro-micro-nano integrated ultra-precision diamond tool.There are high density of nanotwins with an average thickness of 2.51 nm in the indented nickel alloy.The stress inducing nanotwin in nickel alloy was calculated as 3.86 GPa,using cutting model and the critical twinning stress formula.In situ transmission electron microscope(TEM)samples were prepared using focused ion beam(FIB)technology.Mechanical properties were measured using in situ transmission electron microscope(TEM)technology.The stiffness,hardness and strength of the nanotwinned nickel alloy were 9.9,1.8 and 3.6 times of those of traditional nickel alloy.Nanotwinned silicon was fabricated through ultrahigh speed(40 m/s)grinding at depth of nanoscale using single-point diamond tools.The nanotwins fabricated in single crystal silicon are nanotwin superlattices,which are included in a silicon nanostructure containing several layers of single crystal,nanotwin superlattices,slip band and amorphous silicon.The nanotwin layer has a thickness of about 40 nm.The stresses inducing nanotwins in silicon was 5.11 GPa,calculated using cutting model and critical twinning stress formula.Moreover,a new tetragonal phase of silicon was verified in the region between the silp band layer and amorphous layer,by the methods of the TEM characterization and Fourier transformation.The stress of the phase transition calculated using Peirls-Nabarro stress formula and the first principle calculation were 2.06 and 1.59 GPa,respectively.Stress-induced nanotwin was fabricated by the pure machining stress of diamond tool.This novel approach allows for the fabrication of nanotwinned nickel alloy and nanotwinned silicon,without the help of harsh conditions and toxic reagents.It is important to the strengthening of nickel alloy and optoelectronics applications of silicon.Meanwhile,it also paves a new way to fabricate nanotwin in other materials.